As a result of #4670 and the safe decision to not memoize machine.ssh_info (see 89a4a29d65cace4d970d0f220ad01815883ab8aa and 5036d16461cfafde5274836d51b97740c23bd4eb), it is preferable to store the ssh_info hashes and avoid multiple function calls when generating the ansible inventory.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.